Biological De-Inking Method

ABSTRACT

A method of de-inking wastepaper by pulping the paper in the presence of an enzyme is disclosed. The enzyme dislodges the ink particles from the paper fibers. The preferred enzymes are the acid resistant carbohydrases. The de-inking medium is an aqueous solution of the enzyme, preferably maintained at a pH less than about 7 and at a temperature between about 20° C. and about 60° C. No conventional chemical de-inking agents are required. The dislodged ink particles may be removed by any conventional method, such as flotation or washing.

This is a continuation-in-part application of U.S. patent applicationSer. No. 07/518,935 filed May 4, 1990, co-pending herewith and laterabandoned

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for reclaiming useful pulp fibersfrom wood-containing or wood-free wastepaper by a biological method inthe de-inking process.

2. Description of the Background

De-inking of pulp fibers is essentially a laundering or cleaning processin which the ink is considered to be the dirt.

Chemicals, along with heat and mechanical energy, are used to dislodgethe ink particles from fibers and to disperse them in the aqueousmedium. The ink particles are then separated from the pulp fibers,either by washing or flotation or by using a modern hybrid process thatcombines washing and flotation.

The chemicals used for the conventional de-inking process aresurfactants which function as detergents to remove ink from the fiber,as dispersants to keep the ink particles dispersed and preventredeposition on the fibers, and foaming agents in the froth flotation ofink particles.

A typical surfactant is a long chain molecule with a hydrophobic part onone end and a hydrophilic part on the other end. The hydrophobic partmay consist of fatty acid, fatty alcohol, alkylphenols or otheroil-soluble surfactants.

The hydrophilic part in the de-inking surfactant usually consists ofanionic molecules, such as carboxylic acid salts or sulfonic acid saltsand nonionic molecules, such as polyoxyethylenated chains.

The typical surfactants commonly used in the washing and froth flotationde-inking processes are: sodium and potassium salts of straight-chainfatty acids (soaps), linear alkylbenzenesulfonates (LAS), long-chainfatty alcohols, polyoxyethoxylated alkylphenols, alkylphenolethoxylates, and polyoxyethoxylated straight-chain alcohols.

A major disadvantage of using these surfactants in the de-inking processis excess foaming in the subsequent pulp stock flow and paper makingprocess lines. Moreover, some of the above surfactants are resistant tobiodegradation in the effluent treatment stages causing a seriousenvironmental problem.

In the froth flotation de-inking process, collector is added toagglomerate ink into large particles and attach them to the air bubbles.Collectors are required for effective flotation and are usually anioniclong-chain fatty acid soaps. Fatty acid collectors are precipitated withcalcium ions to form larger, insoluble ink particles and collectorparticles. With injection of air in the flotation cells, theagglomerated ink particles adhere to the bubbles, rise to the surfaceand are skimmed off from the system.

Major disadvantages of the flotation method using the fatty acidcollector are a pitch deposition and calcium scaling problems in thesubsequent stock lines and papermaking process equipment. Besidessurfactants, other chemicals employed are caustic soda, sodium silicate,metal ion chelating agents and hydrogen peroxide.

The hydrogen peroxide bleaching agent has to be added in order toprevent pulp yellowing caused by the addition of caustic soda and toimprove the brightness of pulp fibers.

With advances in modern printing and photocopying technology,conventional de-inking with the aid of surfactants encounters seriousproblems because the wastepaper is printed with the use of heavilycoated, highly polymerized or non-impact inks, such as ultraviolet,heatset, Xerox, laser and ink jet. These inks usually contain curedpolymer resins which bind ink particles so strongly on the fiber surfacethat it is impossible to dislodge the inks completely during thewastepaper defiberizing (pulping) stage with the conventional de-inkingchemicals. Excess heat and mechanical energy are also required alongwith the ineffective conventional chemicals.

Furthermore, in the conventional flotation de-inking process fornewsprint wastepaper, a major technical problem has to do with the factthat fine ink particles are embedded in the fiber bundles and betweenfibrils which are almost impossible to be removed from the fibers by awashing and/or flotation process.

SUMMARY OF THE INVENTION

This invention provides a new and much improved de-inking method whichis effective for newsprint as well as wood-free printed wastepaper, suchas whiteledger, laser printed, xerographic copypaper and computerprintout wastepaper.

The de-inking method of the present invention is to remove ink particlesby the use of the biological activity of enzymes on the cellulose fibersurface and the dispersing function of enzyme protein on ink particles.

In contrast to the conventional method, no alkali or de-inkingsurfactants are required. In the froth flotation process, the fatty acidcollectors are not required. Since caustic soda is not used in thenewsprint de-inking, a hydrogen peroxide bleaching agent is also notrequired for preventing yellowing.

The elimination of the fatty acid collector in this biological de-inkingprocess will solve the persistent pitch and scale deposition problemassociated with the conventional flotation process using the fatty acidtype soap and calcium salts and silicates.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The wastepaper, such as old newsprint, is disintegrated in aconventional pulper (consistency 4-7%) or in a high consistence pulper(consistency 12-15%) at a water temperature ranging from about 20° C. upto 60° C. The addition level of enzyme is about 0.005% to about 5.0% byweight based on dry weight of wastepaper. The pH of the stock slurry isin the range of 3.0 to 8.0 preferably below about 7.0, and preferablybetween about of 3.0 and 7.0.

As compared to the conventional pulping process using caustic andsurfactants, the pulping in the presence of enzyme can be completed in arelatively short period and ink particles are completely separated fromthe fiber surface and dispersed well. The dispersed inks are removed outof the pulp fibers by using the conventional washing process equipment,such as vibrating screen and drum washers without the aid of detergentsurfactants in single and multi-stages. The ink particles dispersed withthe action of enzyme protein can be also selectively removed out of thediluted pulp slurry with conventional flotation equipment in which airis injected or drawn into the pulp to provide bubbles to pick up theparticles. No fatty acid collector is required in the case of wastenewsprint. A small amount of fatty acid collector may be added toenhance the ink removal efficiency in the case of laser-printedwastepaper.

Among enzymes which can be used in the method are the carbohydrases andparticular enzymes, such as cellulase, hemicellulase, pectinase andmixtures thereof. Examples of commercially available cellulases usefulin these methods are those derived from Trichoderma viride andAspergillus niger. These and other acid resistant enzymes may be usedalone or as mixtures.

This biological de-inking process lowers pulping energy requirements toa large extent (almost 50% reduction) since the addition of enzymeresults in a substantial reduction in pulping time as compared to thepulping in the absence of enzyme. The observed faster and easier pulpingin the presence of enzyme may be attributed to the unique biologicalactivity of the enzyme which is effective to debond the fiber bondingand dislodge the inks bonded on the fiber surface as well as within thefiber bundles or between the fibrils. A partial enzymatic hydrolysis ofcellulose within the micro structure of the fiber surface may occurduring the pulping stage. Because of this biological activity of theenzyme, the fine ink particles embedded within fiber bundles, fibrilsand fines which have been impossible to be taken out by the conventionalde-inking chemicals in the case of old newsprint de-inking are removed.

According to this biological de-inking method of old newsprint, theaddition of hydrogen peroxide to prevent fiber yellowing is notrequired. This results in a substantial reduction of de-inking chemicalcost as compared to the conventional de-inking process using causticsoda, hydrogen peroxide, chelating agents and sodium silicates.

It should be pointed out that the physical strength properties of theresulting pulp fiber prepared by this inventive method are found to behigher than those of the corresponding pulp prepared by the conventionalmethod in addition to the much higher resulting pulp brightness. Theenzyme addition does not appear to degrade the fiber strength, butrather improves the fiber strength for reasons not presently known.

To more fully illustrate the present invention, the followingnon-limiting examples are presented.

De-Inking of Old Newsprint with a Cellulolytic-Enzyme EXAMPLE 1

A sample of old newsprint wastepaper was added to the pulper which wasfilled with 40° C. water at a consistency of 4% and a cellulose (enzyme)was dissolved at the dosage level of 0.1% based on oven dry weight ofwastepaper. The wastepaper was soaked for 10 minutes and thendisintegrated for 5 minutes. After a complete disintegration ofwastepaper, one half of the pulp slurry was diluted to 1% consistency.

The diluted pulp slurry was moved to the air flotation cell and then thedispersed ink particles were removed out of the pulp slurry by skimmingoff the ink particles froth out of the cell while injecting air througha porous plate. The flotation time for the complete removal of the inkfroth was one minute.

The other half of the pulp slurry was washed on a laboratory vibratingscreen to remove the dispersed ink particles.

The resulting recycled pulp fibers obtained by the flotation and thewashing step were evaluated for pulp brightness and mechanical strengthproperties.

Comparative Example

To compare the foregoing enzyme-treated de-inked pulp to theconventional de-inked pulp, the same sample of wastepaper was treated inthe pulper with addition of 1.0% sodium hydroxide, 0.3% hydrogenperoxide, 3% sodium silicate solution (water glass) and 0.8% of SERFAXMT-90 (fatty acid soap) and 0.2% IGEPAL-660 (biodegradable nonionicsurfactant marketed by GAF Corporation) based on oven dry weight ofwastepaper. The pulping time was 10 minutes for a completedisintegration. After diluting to 1% consistency, the dispersed inkparticles were removed by the flotation method with the laboratoryflotation cell as described above.

TABLE 1 Comparison of properties of recycled pulp by the method of thepresent invention and the conventional method Tensile Index Tear IndexBrightness (%) (N · m/g) (mN · m/g) KONP AONP KONP AONP KONP AONPcellulase 47.1 45.2 28.9 32.4 11.7 13.6 enzyme after 50.3 48.6 29.3 32.911.8 14.1 washing conventional 45.1 38.4 30.1 32.8 10.8 13.1 methodKONP: Korean old newspaper AONP: American old newspaperAs shown in Table 1, the brightness of the pulp de-inked with enzyme wasmuch higher than that of the pulp de-inked with the conventionalchemicals and the mechanical strength of the pulp de-inked with enzymewas also superior to the pulp de-inked with the fatty acid collector andthe dispersant (IGEPAL-660). Microscopic observation revealed that thepulp prepared by the present invention contained more long fiberfractions, has smoother fiber surface and looks less mechanicallydamaged.

As can be seen from the data in Table 1, the enzyme treated pulp gavecleaner and brighter pulp with the washing as compared to the flotationink removal using the conventional method.

Enzyme Concentration Effect on Disintegration Time

The enzyme addition also appeared to accelerate the wastepaperdisintegration to a large extent. When the old newspaper wasdisintegrated in the conventional pulper at the 4% consistency, theaddition of 0.5% enzyme reduced the pulping time from 5 minutes (noenzyme addition) to 30 seconds for a complete disintegration as shown inTable 2.

TABLE 2 Relation between enzyme addition and disintegration time. enzyme(%) 0.5 0.1 0 (cellulase) disintegration time 30>   60-120 300< 

De-Inking of Laser CPO (Computer Printout) with Cellulolytic Enzyme

It is almost impossible to achieve a complete removal of laser beamcured ink particles from the laser CPO wastepaper with conventionalde-inking chemicals, because the ink particles are so strongly adheredto the fiber surface that alkali and general de-inking surfactants usedin the conventional process are not able to dislodge and disperse theink in the pulp-water slurry.

EXAMPLE 2

A sample of laser CPO wastepaper was added to water in a laboratory highconsistency pulper to achieve a consistency of 12.5% and a cellulase(enzyme) was added to the water at the dosage level of 0.2% based on thedry weight of paper. At stock water temperature of 20-35° C., thepulping was carried out for 20 minutes. The completely disintegratedpulp slurry was diluted to 0.5% consistency and then the dispersed inkparticles were removed out of the pulp slurry using the laboratoryflotation cell in the same way described in Example 1. In this case, toincrease the ink removal efficiency and selectivity, a small amount ofthe conventional fatty acid collector, SERFAX MT-90, 0.3% based on dryweight of wastepaper, was added prior to the air flotation step and theflotation time was 3 minutes.

Comparative Example

To compare to the enzyme de-inked pulp, the conventional de-inked pulpwas prepared by the same way, but the following chemicals and conditionswere used:

-   1% NaOH on dry weight of wastepaper-   0.1% IGEPAL-660 dispersant-   0.8% SERFAX MT-90-   50° C. pulping temperature-   30 minutes pulping time-   220 ppm calcium salt addition to the flotation cell-   3 minutes flotation time

The brightness and the strength properties of the resulting pulp sampleswere compared in Table 3.

TABLE 3 Comparison of pulp properties recycled by the method of thepresent invention and the conventional method. Dirt Amount Tensile IndexBrightness (%) (count/area) (N · m/g) enzyme + MT-90 79.0 450 34.3(0.3%) conventional 80.6 4,330 26.3 method + MT-90 (0.8%)

De-Inking of Waste Newsprint by Pectinolytic Enzyme EXAMPLE 3

As per the method of Example 1, the waste newsprint containing 0.1% ofpectinase was soaked for 10 minutes at 40° C. and disintegrated for 5minutes. The disintegrated pulp was diluted to a consistency of 1%. Inkparticles were removed by flotation for 1 minute.

Comparative Example

The procedure of the comparative example of Example 1 above wasrepeated. As shown in Table 4, the brightness and the tensile strengthof paper sheet prepared by the method of the present invention areimproved.

TABLE 4 Comparison of the method of using pectinolytic enzyme with theconventional method Tensile Index Brightness (%) (N · m/g) pectinaseenzyme 44.2 33.3 conventional method 38.4 32.8 MT-90 (0.8%)

The foregoing disclosure and description of the invention isillustrative and explanatory thereof, and various changes in the methodsteps may be made within the scope of the appended claims withoutdeparting from the spirit of the invention.

1-20. (canceled)
 21. A method of de-inking waste printed paper,comprising a) pulping at a pH between 3 and 8 waste printed paper withan enzyme capable of dislodging ink particles from the waste printedpaper in an aqueous medium at a pH between 3 and 8, wherein ink isdislodged from the waste printed paper by action of the enzyme; and b)removing the dislodged ink particles from the resulting pulp containingmedium.
 22. The method of claim 21 wherein dislodged ink particles areremoved by flotation.
 23. The method of claim 21 wherein dislodged inkparticles are removed by washing.
 24. The method of claim 21 wherein theamount of enzyme used is in the range of 0.005 to 5 percent-by-weightbased on the dry weight of the wastepaper.
 25. The method of claim 21,wherein said enzyme is selected from the class consisting of cellulases,pectinases, and mixtures thereof.
 26. The method of claim 21 whereinsaid enzyme is selected from the group consisting of cellulases derivedfrom Trichoderma viride, Aspergillus niger, hemicellulases, othercarbohydrases and mixtures thereof.
 27. The method of claim 21 whereinalkali is not added to the aqueous medium.
 28. The method of claim 21wherein the pulping occurs at a wastepaper pulp consistency of about 12%or greater.
 29. The method of claim 21 wherein the pulping occurs for aperiod of less than about 1 hour.
 30. The method of claim 21 wherein thetemperature of the pulping is in a range of from room temperature up toabout 60 C.
 31. A method of recycling waste printed paper, comprising:a) pulping waste printed paper; b) contacting at a pH between 3 and 8waste printed paper at high wastepaper pulping consistency with anenzyme capable of dislodging ink particles from the waste printed paperin an aqueous medium at a pH between 3 and 8, wherein ink is dislodgedfrom the waste printed paper by action of the enzyme; and c) removingdislodged ink particles from the resulting pulp containing medium. 32.The method of claim 31, wherein the enzyme is a cellulase selected fromthe group of cellulases derived from Trichoderma viride, Aspergillusniger or mixtures thereof wherein the cellulase is used in an amountbetween 0.005 and 5.0 percent-by-weight based on the dry weight of thewaste printed paper, the contacting being carried out at a temperaturebetween room temperature and about 60° C.
 33. The method of claim 31wherein the amount of enzyme used is in the range of 0.005 to 5percent-by-weight based on the dry weight of the wastepaper.
 34. Themethod of claim 31 wherein said enzyme is selected from the classconsisting of cellulose, pectinase, and mixtures thereof.
 35. The methodof claim 31 wherein said enzyme is a cellulase-selected from the groupconsisting of cellulases derived from Trichoderma viride, Aspergillusniger, hemicellulases, other carbohydrases and mixtures thereof.
 36. Themethod of claim 31 wherein the ink particles are removed by flotation orwashing.
 37. The method of claim 31 wherein alkali is not added to theaqueous medium.
 38. The method of claim 31 wherein the pulping occurs ata wastepaper pulp consistency of between 12% and 15%.
 39. The method ofclaim 31 wherein the pulping occurs for a period of less than about 1hour.
 40. The method of claim 31 wherein the temperature of the pulpingis in a range of from room temperature up to about 60 C.
 41. A method ofbiologically de-inking waste printed paper comprising: a) pulping thewaste printed paper with an enzyme capable of dislodging ink particlesfrom the waste printed paper in an aqueous medium at an acidic range orneutral range pH, and wherein the ink is dislodged from the wasteprinted paper by action of said enzyme; and b) removing dislodged inkparticles from the resulting pulp containing medium.
 42. The method ofclaim 31 wherein the enzyme enhances removal of materials selected fromthe group consisting of heavily coated inks, highly polymerized inks,non-impact inks, and cured polymer resins.
 43. The method of claim 42wherein the enzyme is effective to enhance removal of cured polymerresins.
 44. The method of claim 31 wherein the enzyme is effective todebond fiber bonding.
 45. The method of claim 25 wherein the enzymedegrades by enzymatic hydrolysis.
 46. The method of claim 31 wherein theenzyme degrades by enzymatic hydrolysis.
 47. The method of claim 41wherein the enzyme degrades by enzymatic hydrolysis.
 48. The method ofclaim 21 wherein the enzyme is an acid resistant cellulase.
 49. Themethod of claim 21 wherein the wastepaper is disintegrated in aconventional pulper.
 50. The method of claim 49 wherein the consistencyof the pulp in the conventional pulper is between 4 and 7%.